The present invention relates to improved pressure-sensitive adhesive compositions.
The present invention further relates to improved readily removable and repositionable pressure-sensitive adhesive compositions.
The present invention also further relates to a readily removable and repositionable polymeric based pressure-sensitive adhesive composition incorporating a halo-organophosphorous plasticizer.
The present invention still further relates to a readily removable and repositionable polymeric-based pressure-sensitive adhesive composition that is suitable for thin adhesive film applications to paper, or other laminar backing materials, for easy application to and removal from a variety of substrate surfaces.
A pressure-sensitive adhesive that is to be used in the thin adhesive film applications of the present invention must exhibit characteristics of good tensile strength and cohesion, and must possess sufficient adhesiveness or tack, in order to bind a laminar backing material to a substrate surface upon the application of pressure. Further, it must be removable from the other substrate surface without the deposition of a gummy adhesive residue and without damage to the substrate surface.
It is well known in the adhesive art that certain copolymers or copolymer blends are useful as adhesives. Removable or repositionable pressure-sensitive adhesive compositions, based on a plasticized polyvinyl chloride polymer or polyvinyl chloride/polyvinyl acetate copolymer have been in existence for quite some time. U.S. Pat. No. 3,300,543, issued to Turner, describes such an adhesive composition.
In addition, there are on the market, vinyl films having a coating exhibiting a very low tack characteristic, which will readily adhere to and be removable from a variety of very smooth substrate surfaces.
However, when paper labels, or the like laminar backing materials, which are coated on one side with these prior art adhesive compositions, are applied to a paper or another laminar substrate surface having low delamination strength, either the paper label won't readily adhere to the paper, or other substrate surface, or alternatively, it becomes very difficult to remove the label after a brief period of contact time, without tearing the label and/or the substrate paper.
Tack may be described as a measure of the strength or agressiveness with which an adhesive bonds to a surface. The Polyken Probe Tack Tester.RTM. (trademark for apparatus for measuring tack made by The Kendall Company), which measures the `unbonding` strength of an adhesive from a stainless steel probe surface after a short dwell time on that surface. Tack will vary not only with dwell time, but also with the nature of the adherent surface (i.e. glass, paper, skin, etc.), as well as the finish of the surface (i.e. smooth, matte, wet, etc.). The amount of pressure that is required to be applied in order to form the adhesive bond is also important.
Peel strength, on the other hand, is the unbonding strength measured after a longer dwell time of the adhesive on a surface. One standard method applies a pressure of a 4.5 pound rubber roller and a dwell time of 15 minutes .+-.5 minutes. The adhesive tape is then peeled away at a rate of 12 inches per minute, and at a 180.degree. angle.
In the present invention, it has been a desirable object to maximize the tack meanwhile maintaining a certain minimum peel value, such that the laminar backing material will not "butterfly", or peel off the substrate, before sufficient adhesive bond strength is achieved.
On the other hand, in certain applications, a maximum peel strength value may be desirable so that the laminar backing will not cause delamination of the application surface during the unbonding process. On the other hand, if the strength of the laminar backing and the substrate surface is strong enough, peel strength values could be higher in order to maintain good removability of the tape.
The proper balance of adhesion and tack with ready removability (peel) of the laminar backing material has been found to be difficult to achieve.
In the present invention, it has been surprisingly determined that by incorporating optimal concentration ratios of a polyester plasticizer and a halo-organophosphorous plasticizer into a plasticized vinyl copolymer, here a copolymer of vinyl chloride-vinyl acetate, better cohesive control with desired plasticity and preferred tack characteristics of the resultant pressure-sensitive adhesive composition could be readily achieved.
It was further found that high concentrations of the polymeric polyester plasticizer component, along with low concentrations of the halo-organophosphorous plasticizer component, resulted in a pressure-sensitive adhesive having high tack; however, poor cohesive strength also resulted. In contra-distinction, in a composition having a high concentration of the halo-organophosphorous plasticizer component, and low concentrations of the polymeric polyester plasticizer component, an essentially nontacky adhesive, having a good cohesive strength, was obtained.
The present invention has resulted in the determination of the optimum concentration ratio of both the polyester plasticizer and halo-organophosphorous plasticizer components in the pressure-sensitive adhesive in order to produce an adhesive film composition having the optimum balance of tack, adhesion, film integrity, softness, and removability.